Nanoparticles are being widely investigated for bio-medical applications. The possibility to manipulate and control magnetic properties of magnetic nanoparticles leads to diverse applications in diagnosis, disease treatment and even disease detection. As more and more uses of nanoparticles for in-vivo applications emerge, concerns on their toxicity are raised.
Biodegradable nanoparticles will find use for imaging, cell tracking, drug delivery, cancer therapy et al. A few attempts at making biodegradable nanoparticles are reported, for instance, luminescent porous silica particles in micrometer size. Composite particles made of 4-5 nm Au nanoparticles are also considered biodegradable since they decompose into small clusters that then get cleared out from the body. Although iron oxide magnetic nanoparticles are sometimes considered degradable, evidence for this is not fully established. In addition, the residence time of iron oxide nanoparticles inside the body is long.
There has been burgeoning interest in magnetic hyperthermia because of its potential in cancer treatment with minimized side effects. Under high frequency, targeted, AC magnetic field excitation, heat released from magnetic nanoparticles would lead to degradation of malignant cells. With a large number of heat sources spreading around the targeted area, working efficiency is expected to be high. In this circumstance, precise control of temperature in the safe working range is a challenge. How localized the heat profile can be and how accurate a device can sense in-vivo temperature and control on/off performance are challenges for magnetic hyperthermia.
Interest in materials for self-regulated magnetic hyperthermia is emerging. The goal is to use the ferromagnetic transition temperature to achieve self-regulation. Magnetic materials with Curie temperature close to the safe working range of 42° C.-49° C. have been investigated, including Ni doped Cu, La1-xSrxMnO3, Fe—Ni based alloy and Zn ferrite. Although the materials have suitable Curie temperature, most of them have low saturation magnetization, which affects heating efficiency greatly. There are also concerns of the biocompatibility of these materials.
Mesoporous silica nanoparticles (MSNP) are a multifunctional delivery platform that has been shown at cellular and in vivo levels to be capable of delivering drugs such as chemotherapeutic agents and DNA/siRNA to a variety of cancer cell types (Lu et al., Small, vol. 3, pp. 1341-1346, 2007; He et al., Small, vol. 7, pp. 271-280, 2011; Lee et al., Adv. Funct. Mater., vol. 19, pp. 215-222, 2009; Liong et al., ACS Nano, vol. 2, pp. 889-896, 2008; Meng et al., ACS Nano, vol. 4, pp. 4539-4550, 2010; Meng et al., J. Am. Chem. Soc., vol. 132, pp. 12690-12697, 2010; Xia et al., ACS Nano, vol. 3, pp. 3273-3286, 2009; Radu et al., J. Am. Chem. Soc., vol. 126, pp. 13216-13217, 2004; Slowing et al., J. Am. Chem. Soc., vol. 129, pp. 8845-8849, 2007). This delivery platform allows effective and protective packaging of hydrophobic and charged anticancer drugs for controlled and on demand delivery, with the additional capability to also image the delivery site (Liong et al., ACS Nano, vol. 2, pp. 889-896, 2008). The key challenge now is to optimize the design features for efficient and safe in vivo drug delivery (He et al., Small, vol. 7, pp. 271-280, 2011; Lee et al., Angew. Chem. Int. Ed., vol. 49, pp. 8214-8219, 2010; Liu et al., Biomaterials, vol. 32, pp. 1657-1668, 2011; Al Shamsi et al., Chem. Res. Toxicol., vol. 23, pp. 1796-1805, 2010), which can be assessed through the use of human xenograft tumors in nude mice (Lu et al., Small, vol. 6, pp. 1794-1805, 2010).
Based on properties such as large surface area and porous channels that can be used to encapsulate molecules, mesoporous silica nanoparticles (MSNP) have emerged as an efficient drug delivery platform (Kim et al., Angew. Chem., Int. Ed., vol. 47, pp. 8438-8441, 2008; Liong et al., ACS Nano, vol. 2, pp. 889-896, 2008; Lu et al., Small, vol. 3, pp. 1341-1346, 2007; Slowing et al., Adv. Drug Delivery Rev., vol. 60, pp. 1278-1288, 2008; Vallet-Regi et al., Angew. Chem., Int. Ed., vol. 46, pp. 7548-7558, 2007). In addition to the well-developed surface chemistry, silica materials are known to be safe, biodegradable and potentially biocompatible (Borm et al., Toxicol. Sci., vol. 90, pp. 23-32, 2006; Finnie et al., J. Sol-Gel. Sci. Techn., vol. 49, pp. 12-18, 2009). This drug transport system is suitable for the delivery of anticancer drugs, including camptothecin, paclitaxel, and doxorubicin (Kim et al., Angew. Chem., Int. Ed., vol. 47, pp. 8438-8441, 2008; Liong et al., ACS Nano, vol. 2, pp. 889-896, 2008; Vivero-Escoto et al., J. Am. Chem. Soc., vol. 131, pp. 3462-3463, 2009). The chemical stability of the particles contribute to their therapeutic utility by allowing the attachment of functional groups for imaging and targeting applications along with the placement of a series of nanovalves for on-demand drug release (Liong et al., ACS Nano, vol. 2, pp. 889-896, 2008; Nguyen et al., Org. Lett., vol. 8, pp. 3363-3366, 2006; Rosenholm et al., ACS Nano, vol. 3, pp. 197-206, 2009).